Aren't people in the US arguing about the legality of actions by ICE?

Not everything anyone does to address a murder is legal.

Murder should be addressed by doing exactly what the text of the law says ought to be done (at the time of the act, or the prosecution, whichever is the most lenient).
If a policeman just shoots me because I am a murderer (not to *prevent* a crime, to punish the crime), now you have two murderers.